how to create javalin user registration and login

 To create user registration and login functionality in Javalin, follow these steps:

1. User Registration Endpoint

For user registration, we need an endpoint that allows a user to create a new account by sending a POST request with username and password.

Steps:

  1. Validate the input:
    • Username must not be blank.
    • Password must be at least 4 characters long.
    • Ensure the username is unique.
  2. Save the user to the database if all conditions are met.
  3. Return a success response with the created account or an error message if validation fails.

2. User Login Endpoint

For user login, we need an endpoint that allows a user to log in by sending a POST request with their username and password.

Steps:

  1. Validate the input:
    • Check if the username and password match an existing account.
  2. If successful, return the account details. Otherwise, return an error response.

Implementation: Controller for Registration and Login

Here’s how you can implement these endpoints in your Javalin controller:

java
import io.javalin.Javalin;
import io.javalin.http.Context;

public class UserController {

    private final AccountService accountService;

    public UserController(AccountService accountService) {
        this.accountService = accountService;
    }

    public void registerEndpoints(Javalin app) {
        app.post("/register", this::registerUser);
        app.post("/login", this::loginUser);
    }

    private void registerUser(Context ctx) {
        try {
            // Parse the incoming request body into an Account object
            Account account = ctx.bodyAsClass(Account.class);

            // Call the service layer to handle registration
            Account createdAccount = accountService.registerAccount(account);

            if (createdAccount != null) {
                ctx.status(200).json(createdAccount); // Successful registration
            } else {
                ctx.status(400).result("Invalid input or user already exists.");
            }
        } catch (Exception e) {
            ctx.status(400).result("Failed to register user: " + e.getMessage());
        }
    }

    private void loginUser(Context ctx) {
        try {
            // Parse the incoming request body into an Account object
            Account account = ctx.bodyAsClass(Account.class);

            // Call the service layer to handle login
            Account loggedInAccount = accountService.login(account.getUsername(), account.getPassword());

            if (loggedInAccount != null) {
                ctx.status(200).json(loggedInAccount); // Successful login
            } else {
                ctx.status(401).result("Invalid username or password."); // Unauthorized
            }
        } catch (Exception e) {
            ctx.status(400).result("Failed to login: " + e.getMessage());
        }
    }
}

Service Layer Logic

Ensure the AccountService includes logic for registration and login:

AccountService

java
public class AccountService {

    private final AccountDao accountDao;

    public AccountService(AccountDao accountDao) {
        this.accountDao = accountDao;
    }

    public Account registerAccount(Account account) {
        // Validation
        if (account.getUsername() == null || account.getUsername().isEmpty()) {
            return null; // Username cannot be blank
        }
        if (account.getPassword() == null || account.getPassword().length() < 4) {
            return null; // Password must be at least 4 characters
        }
        if (accountDao.getAccountByUsername(account.getUsername()) != null) {
            return null; // Username already exists
        }

        // Save to the database
        return accountDao.createAccount(account);
    }

    public Account login(String username, String password) {
        Account account = accountDao.getAccountByUsername(username);

        if (account != null && account.getPassword().equals(password)) {
            return account; // Valid credentials
        }
        return null; // Invalid username or password
    }
}

Model Classes

Account.java

java
public class Account {
    private int accountId;
    private String username;
    private String password;

    public Account() {}

    public Account(int accountId, String username, String password) {
        this.accountId = accountId;
        this.username = username;
        this.password = password;
    }

    // Getters and setters
    public int getAccountId() {
        return accountId;
    }

    public void setAccountId(int accountId) {
        this.accountId = accountId;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

Database Interaction

Ensure the DAO layer provides methods to handle account persistence:

AccountDao.java

java
public class AccountDao {

    public Account createAccount(Account account) {
        String sql = "INSERT INTO Account (username, password) VALUES (?, ?) RETURNING *";
        try (Connection conn = ConnectionUtil.getConnection();
             PreparedStatement ps = conn.prepareStatement(sql)) {

            ps.setString(1, account.getUsername());
            ps.setString(2, account.getPassword());

            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                return new Account(
                        rs.getInt("account_id"),
                        rs.getString("username"),
                        rs.getString("password")
                );
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public Account getAccountByUsername(String username) {
        String sql = "SELECT * FROM Account WHERE username = ?";
        try (Connection conn = ConnectionUtil.getConnection();
             PreparedStatement ps = conn.prepareStatement(sql)) {

            ps.setString(1, username);

            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                return new Account(
                        rs.getInt("account_id"),
                        rs.getString("username"),
                        rs.getString("password")
                );
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
}

Running the App

  1. Create and set up the database with the Account table using the provided SQL script.
  2. Configure the database connection using a ConnectionUtil class.
  3. Start the Javalin app and test the endpoints using tools like Postman or cURL.

Testing the Endpoints

Register User:

Request:

json
POST http://localhost:8080/register
{
    "username": "testuser",
    "password": "12345"
}

Response:

json
{
    "accountId": 1,
    "username": "testuser",
    "password": "12345"
}

Login User:

Request:

json
POST http://localhost:8080/login
{
    "username": "testuser",
    "password": "12345"
}

Response:

json
{
    "accountId": 1,
    "username": "testuser",
    "password": "12345"
}

Invalid Credentials Response:

json
401 Unauthorized
{
    "message": "Invalid username or password."
}

Would you like help testing these endpoints or adding advanced features?

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